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Bill to encourage rooftop gardens on new San Francisco buildings


From the sidewalk, the Whole Foods building on upper Market Street looks like any other sleek new development. But there’s a difference on the roof, where a lush garden provides an oasis.

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Imagine gardens like that one on rooftops across San Francisco, a collection of green spaces reaching into the air. San Francisco Supervisor Scott Wiener plans to introduce legislation that aims to do just that, according to the San Francisco Chronicle.

It builds on a law the Board of Supervisors passed in April that requires new residential and commercial buildings 10 stories or shorter to install electricity-generating solar panels or a solar heating system that covers 15 percent of the roof. Wiener, who introduced the law, said it was the first of its kind in the country.

His new legislation would allow green roofs, also known as living roofs, to fulfill the solar requirement. Essentially, for every square foot intended for solar energy, there would have to be 2 square feet of green space — the idea being that at that calculation the two options would cost roughly the same.

Developers could also combine solar and green roof space to meet their obligations. The Federal Office Building at 50 United Nations Plaza in the Civic Center has such a mix.

“The solar requirement and the green roof requirement have always been two peas in a pod,” Wiener said. “They make roofs more environmentally sustainable, cities more environmentally sustainable, and take a very underutilized space to either create clean energy or help us with energy efficiency.”

Green roofs can vary depending on their depth and type of potting soil. Broadly speaking, they include water retention and drainage systems, a waterproofing membrane and plants.

An October 2013 study by the urban think tank SPUR on the benefits of green roofs identifies their benefits: reduced storm water runoff, food production through community gardens, improved air quality, better views and an increase in habitat that improves biodiversity.

To date, roughly 45 large-scale developments have green roofs, according to the San Francisco Planning Department, and at least 10 more projects are in the works.

They’re not inexpensive. Jeff Joslin of the Planning Department said they tend to cost $10 to $30 per square foot.

A June 2016 study by the consulting firm ARUP Group that looked at the costs and benefits of green roofs in San Francisco concluded that “owners tend to bear all costs for living roofs, even though the community receives many of the benefits.”

Without the use of incentives and other policy investments, the report said, “San Francisco is unlikely to see as rapid an increase in living roof areas as would be preferred for community benefits.” Wiener’s law includes no incentives.

Several European countries and cities in the United States have embraced the use of incentives.

Germany has had a green roof industry for 40 years, according to the SPUR report, with 70 cities there offering “direct financial incentives” and 150 cities requiring green roofs on new construction. Switzerland offers subsidies for green roof installation. Chicago had a three-year grant program that offered a subsidy of $5,000 per project, in an effort to cool the city during the summer.

Wiener’s legislation appears to be the closest a major city in the United States has come to requiring green roofs.

Supporters of the proposal hope that it will make a dent in the city’s problematic storm drain system, which feeds into the city’s sewers. When it rains heavily, the storm drains overwhelm the sewage system, causing waste to be released into the ocean and bay. The idea is that green roofs will absorb some of the rainwater and slow the passage of water into the drain system, helping prevent runoff.

Even if it should pass, it will be a long time before San Francisco’s roofs will offer a landscape of greenery.

The ARUP study concluded that if 25 percent of new developments install living roofs, that after five years between 1 percent and 7 percent of city roofs in the city would be green.

That doesn’t deter city officials. Bottom line, said Barry Hooper, a green building specialist with the city’s Department of the Environment: “One thing that doesn’t make sense anymore is just wasting that space.”
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Source: proudgreenbuilding


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